This study investigates the use of various features of noun phrases employed in argumentative writing by Saudi college students, as well as differences in the complexity of these noun phrases between learners with varying levels of writing proficiency. Using the hypothesized developmental progression index proposed by Biber et al. (2011), the researcher analyzed argumentative essays to determine prenominal and postnominal modifiers. Additionally, manual coding of data was utilized to document and analyze the occurrence of noun premodifiers and postmodifiers. It was revealed that level-three students relied primarily on attributive adjectives and possessive nouns as premodifiers, whereas the most commonly used phrasal features for level-five students were of- phrases as noun modifiers and nouns as nominal pre-modifiers. The results of the study support the proposed developmental index by demonstrating that level-three students, who are less proficient, heavily relied on attributive adjectives. This finding aligns with the notion that attributive adjectives are acquired at an early stage. Furthermore, the utilization of noun modifiers by level-five students, who belong to the more proficient group, exhibited a much higher resemblance to the frequencies observed in published academic prose compared to the usage by the less proficient group. The results of the study have the potential to contribute to a better understanding of the complexity of noun phrase use among Saudi EFL students' learning.